1. Field of the Invention The present invention relates to an antenna device.
2. Description of the Related Art
An antenna device including a triplate line, in which a central conductor plate is interposed between two ground plates, as a feed line has been developed as an example of an antenna device having a simple structure with which loss in the feed line can be reduced (see, for example, Japanese Unexamined Patent Application Publication No. 63-88902).
With the antenna device including the triplate line as the feed line, in the case where the antenna device is a frequency-sharing antenna capable of transmitting and receiving signals in a plurality of frequency bands, the feed line is required for each frequency band and each polarization. When all of the feed lines are assembled in a single triplate line, the triplate line has an extremely large area, and the size of the antenna device is increased.
Accordingly, the assignee of the present invention has proposed an antenna device including multiple triplate lines that are connected together so as to cross each other.
However, with the proposed antenna device, there is a risk that a contact failure will occur in a section where the ground plates of the triplate lines are connected to each other and intermodulation (IM) distortion will be increased.